Objectives: Primary 1. To measure the uptake of [11C]N-desmethyl-loperamide ([11C]dLop) using PET imaging as a marker of P-glycoprotein function in patients with intracranial gliomas Secondary 1. Correlate [11C]dLop PET uptake with perfusion MRI parameters and FDG PET uptake for volumes of interest (VOI) determined by the baseline MRI. 2. Develop exploratory data for the correlation of [11C]dLop PET imaging with patient outcomes such as response to therapy, survival, and neurotoxicity 3. Develop exploratory data for the correlation of [11C]dLop PET imaging with immunohistochemical and molecular genomic assays of MDR1 and Pgp Eligibility: Patients with predominantly non-enhancing intracranial gliomas will be eligible. Design: This is a pilot study of [11C]dLop PET imaging in 10 patients with intracranial glioma. Standard uptake values (SUVs) corrected for cerebral blood flow determined by [15O]H20 PET scans will be correlated to DCE-MRI (obtained within prior 2 weeks) and FDG-PET (obtained within 4 weeks) to characterize locoregional differences in Pgp function. When available, correlative studies performed on archived tumor tissue acquired immediately subsequent to [11C]dLop scanning will include immunohistochemical assays of Pgp expression, as well as characterization of MDR1 polymorphisms. Patient case histories will be followed longitudinally to make observations about how [11C]dLop imaging may correlate with patient outcomes such as response to therapy, survival, and neurotoxicity.